1. Field of the Invention
The present invention relates to a deflection yoke device provided with a compensation coil which comprises a cylindrical bobbin, coils wound around the bobbin and a magnetic core installed in the bobbin, wherein a misconvergence is compensated by displacing the core to an optimum position in the bobbin.
2. Description of the Related Art
FIG. 1 is a perspective and partially cutaway view a deflection yoke device in the prior art;
FIG. 2 is a perspective view showing a compensation coil shown in FIG. 1;
FIG. 3 is a sectional view showing the compensation coil shown in FIG. 2.
In FIG. 1, a pair of horizontal deflection yoke coils 3a, 3b and a pair of vertical deflection yoke coils 2, each wound in a saddle shape, are respectively provided on inner and outer surfaces of a separator 1 having a cone shape for supporting these vertical and horizontal deflection yoke coils 3a, 3b and 2 and for electrically insulating the vertical and horizontal deflection yoke coils 3a, 3b and 2 from each other. Further, an outside of the vertical deflection coils 2 is covered by a core 4 having a cone shape and made of a magnetic material such as ferrite.
In the deflection yoke device, it is needed a circuit for compensating a deflection characteristic. A printed circuit board 5 for mounting such a circuit and electric parts is provided on a side portion of the separator 1, for instance, being extended from a first flange section 1a having a large diameter to a second flange section 1b having a smaller diameter.
On the printed circuit board 5, there are defined a plurality of approximately rectangular holes 5a. The printed circuit board 5 is fixed on a side section of the separator 1 by causing an end thereof to engage with an engage section 1a1 integrally formed on the first flange section 1a and causing the rectangular holes 5a to engage with nails 1b1 integrally formed on the second flange section 1b.
On the printed circuit board 5, there is also mounted a compensation coil 7 for compensating a misconvergence as explained hereinafter. Specifically, the compensation coil 7 is fixed on the printed circuit board 5 by causing nails 7a formed at distal ends thereof in a longitudinal direction to be engaged with the rectangular holes 5a, 5a of the printed circuit board 5.
Further, on the second flange section 1b, there is provided a compensation coil 6 having four poles for compensating a coma error, so-called VCR. Here, a reference character 9 denotes a connector for connecting the deflection yoke device to a power source (not shown).
Furthermore, on the printed circuit board 5, there are erected plural terminals 8 for connecting leads 2' of the vertical deflection coil 2, leads 3a', 3b' of the horizontal deflection coils 3a, 3b, and lead 6' of the compensation coil 6, and lead 9' of the connector 9 by soldering (not shown).
Here, a description is given of a construction and an operation of the compensation coil 7.
As shown in FIG. 2, the compensation coil 7 comprises a bobbin 10, coils 11, 12 and a core 13. On the bobbin 10 made of an insulative material, there are wound a first coil 11 between the flanges 10b, 10c to be electrically connected to the horizontal deflection coil 3a and a second coil 12 between the flanges 10d, 10e to be electrically connected to the horizontal deflection coil 3b.
In the bobbin 10, there is defined a cave 10a having an approximately cylindrical shape in a longitudinal direction of the bobbin 10. In the cave 10a, there is fitted a core (referred to as a screwed core hereinafter) 13 having an external thread on an outer surface thereof.
As shown in FIG. 3, plural projection ribs 15 are integrally formed on the inner surface of the cave 10a of the bobbin 10 being extended in the longitudinal direction of the bobbin, and the screwed core 13 is forcibly engaged with the ribs 15 of the cave 10a in the bobbin 10.
Further, the screwed core 13 is defined with a hexagonal hole 13a penetrating in the longitudinal direction of the bobbin 10.
FIG. 4 is a sectional view of the compensation coil for explaining an installment operation of a screw core to a bobbin of the compensation coil manually;
FIG. 5 is a sectional view of compensation coil for explaining the installment operation of the screw core to the bobbin of the compensation coil automatically;
FIG. 6 is a sectional view of the compensation coil for explaining the installment operation of the screw core to the bobbin of the compensation coil;
FIG. 7 is a circuit for connecting the horizontal deflection coils 3a, 3b and the compensation coils 7, 70, 71, 72 and
FIG. 8 is a misconvergence pattern which is compensated by the compensation coils.
In FIG. 4, a reference character 14 designates a jig for rotating the screwed core 13. The distal end of the jig 14 is made to be hexagonal to allow the distal end to be inserted into the hexagonal hole 13a of the screwed core 13. When the screwed core 13 is manually screwed into the cave 10a from, for instance, the left side of the bobbin 10 with the jig 14, the screwed core 13 is installed in the bobbin 10, cutting a thread on the projection rib 15. For simplicity, the thread is not depicted in FIG. 4.
In FIG. 4, the screw core 13 is manually installed in the bobbin 10. However, in the mass production the screwed core 13 is automatically inserted into the bobbin 10 by an automatic machine.
In FIGS. 5 and 6, a reference character 16 denotes an automatic machine for inserting the screwed core 13 into the cave 10a by rotating the screw core 13. The distal end 16a of the automatic machine 16 has a hexagonal shape to allow the distal end to be inserted into the hexagonal hole 13a of the screw core 13.
As shown in FIG. 5, first, the screwed core 13 is screwed into the cave 10a from one end of the bobbin 10. Then, the screwed core 13 is transferred being screwed in until another end of the bobbin 10. Thereby, an internal thread is cut on the projection rib 15 in a longitudinal direction of the bobbin 10.
Next, the screwed core 13 is rotated in a reverse direction so that the screwed core 13 is approximately positioned at a center of the bobbin 10 in the longitudinal direction as shown in FIGS. 2 and 4.
The compensation coil 7 constructed as mentioned above is installed on the deflection yoke device as explained referring to FIG. 1, and is electrically connected to the horizontal deflection coils 3a, 3b as shown in FIG. 7.
Specifically, the horizontal deflection coils 3a, 3b are connected in parallel to each other and between a plus terminal (+) and a minus terminal (-), and coils 11, 12 of the compensation coil 7 are connected in series to each other and between the horizontal deflection coils 3a, 3b as shown in FIG. 7. Upon operation, the currents Ia, Ib flow through the horizontal deflection coils 3a, 3b, respectively.
Upon a delivery inspection, the abovementioned deflection yoke device is mounted on an inspection CRT to allow the adjustment of the deflection characteristics as mentioned hereinafter. Further, the inspection CRT refers to a CRT designated by a maker, so-called ITC (Integrated Tube Component) maker which sells such a deflection yoke device combined with a CRT characteristically matched to the deflection yoke.
Before delivering the deflection yoke device to the ITC maker, the deflection yoke device is mounted on the inspection CRT as shown in FIG. 1, and a worker differentially changes the inductances L11 and L12 of the coils 11 and 12 by rotating and transferring the screw core 13 in a B-B' direction as shown in FIG. 4 and 17.
Thereby, the currents Ia and Ib flowing through the horizontal deflection coils 3a, 3b are adjusted, and a magnetic field generated by the horizontal deflection coils 3a, 3b is controlled. As a result, a displacement amount Xv of a red line from a blue line, which is one of the misconvergences shown in FIG. 8, is compensated.
In the ITC maker, the delivered deflection yoke devices are installed on mass-produced CRTs. There may be a slight difference in electric characteristics between the inspection CRT and the mass-produced CRTs. Thus, the ITC maker adjusts again the position of the screw core 13 of the deflection yoke device mounted on the CRT (hereinafter referred to as an ITC state) to eliminates the misconvergence generated on a display of the CRT by rotating the screw core 13 with the jig 14 as shown in FIG. 4.
Then, adjusted CRTs in the ITC state are delivered to, for instance, computer display instrument makers.
When the deflection yoke devices are transported to the ITC maker by vehicles, vibration may be applied to the deflection yoke devices, thus to the compensation coils 7 for a long time. The vibration causes a problem that the screw core 13 is displaced in the cave 10a in the B-B' direction as shown in FIGS. 4 and 7.
When the position of the screw core 13 is displaced, the adjusted deflection characteristic of the deflection yoke device is largely changed, which causes a problem of re-adjustment, resulting in a loss time. In the worst case, the screw core 13 is slipped off from the bobbin 10.
Further, when the deflection yoke devices are transported to display instrument makers, the same vibration is applied to the deflection yoke devices, resulting in the same problem mentioned above.
In order to solve the problems, there is proposed a method in Japanese Patent laid-open Publication 7-220659, wherein the screw core 13 is fixed by using an adhesive after the adjustment of the deflection characteristic of the deflection yoke device. However, as the screw core 13 is tightly fixed by applying the adhesive, it is necessary to apply the adhesive to the screw core 13 at the latest adjustment stage in the manufacturing process.
Further, applying the adhesive to the screw core means an extra production process. This causes a problem of decreasing a working efficiency.
In addition, there are other problems as follows.
As mentioned in the foregoing, in the deflection coils 7 in the prior art, the screw core 13 is screwed into the cave 10a of the bobbin 10. Thereby, the internal thread is cut on the projection ribs 15. Thus, the shape of the internal thread cut on the projection ribs 15 does not maintain a constant shape due to a dispersion of a dimension (height) of the projection rim 15 caused by the dispersion of the resin mold conditions and a dispersion of an outer diameter of the screw core 13. As a result, the rotational torque for rotating the screw core 13 becomes erratic.
Accordingly, as explained referring to FIGS. 5 and 6, upon cutting the internal thread on the projection ribs 15 by the automatic machine 16, it is necessary to adjust an optimum rotational number for rotating the screw core 13 and an optimum reciprocal movement number for reciprocating the screw core 13 in the cave b1a every time when the internal thread is cut on the projection ribs 15 of the bobbin 10 because the optimum numbers of core rotation and of repetition of movement of the screw core 13 are obliged to change for every bobbin 10. The dispersion of required torque of the screw core 13 makes it difficult to further adjust the position of the screw core 13 in the alignment process.
Further, when a height of the projection ribs 15 becomes too high or the outer diameter of the screw core 13 becomes too large, not only the rotational torque becomes large but also chipping and crack are apt to be developed on the screw core 13. When the screw core 13 is repeatedly rotated, the projection ribs 15 are broken to reduce the rotational torque for rotating the screw core 13. This causes a problem that the screw core 13 can no longer be held at a desired position.